Spine IK

Controlling entire spine with Unity IK, may be useful in the future:

https://www.youtube.com/watch?v=gsVZOpMia7w

Aiming Without IK

Aiming by controlling the character's spine or chest bone without using Unity IK:

https://www.youtube.com/watch?v=6UgB7TMk3Bg

Controlling individual bones of a skeleton can be a useful alternative to Unity IK when only a simple solution is needed.

Foot Placement

More on foot placement/planting with Unity IK for the future. Some of these are too advanced for me to grasp at the moment, others may be very heplful as an introduction:

https://www.youtube.com/watch?v=NKIZCPenIas

https://www.youtube.com/watch?v=5eDt-bh9OTY

https://www.youtube.com/watch?v=MonxKdgxi2w

Sharp Accent 3rd-Person Tutorials

These are all of the tutorials from SharpAccent regarding 3rd-person character controllers:

https://www.youtube.com/channel/UCq9_1E5HE4c_xmhzD3r7VMw/playlists?shelf_id=10&sort=dd&view=50

They deal with climbing systems, 3rd-person shooters, and advanced 3rd-person character controllers. They will be integral in going into more depth on creating character controllers for 3rd-person games/shooters with advanced mobility mechanics.

To get started with the Advanced 3rd-person controller:
https://www.youtube.com/watch?v=3YTR_9_Trsg&list=PL1bPKmY0c-wnvW9F4BDJMwDHmq2SQ8m3L

More on foot placement with Unity IK:
https://www.youtube.com/watch?v=5eDt-bh9OTY

FPS and Climbing

This youtuber has many tutorials to do with First Person Shooters in Unity, as well as a climbing system tutorial series:

Main page:
https://www.youtube.com/channel/UCOTOF6DP6XxeBnyLRCS46kA

Climbing system:
https://www.youtube.com/playlist?list=PLZcQtrQ9JcLxzUwz1VvabjOVD64v1ixOG

Will I create a climbing system for my game? No, but I at least want a ledge grab, if I can fit it in, and for my character to grab or strike other objects. Also, the concepts behind these tutorials will be helpful in learning about and implementing Unity IK.

Unity IK Gotchas

This guy explains all of the problems that can happen when trying to get Unity IK, Animation Layers, and other features of Unity Mecanim to work together:

https://www.youtube.com/watch?v=RfQUosJh2DU

This one will be essential to troubleshooting problems that can occur when working with Unity Mecanim.

Sharp Accent Intro to IK

A helpful introduction to Unity IK, though I have not been able to implement the foot planting, and he gets into other advanced applications of Unity IK as well. I have a feeling that this one will be helpful in the future:

https://www.youtube.com/watch?v=EggUxC5_lGE

This is another youtuber that I highly recommend for getting tutorials for scripting and animation within Unity, though his are more advanced.

Unity Documentation, IK

Unity documentation on Unity IK. This one has been helpful in getting me started with Unity IK, as I have been having some trouble grasping it to begin with.

https://docs.unity3d.com/Manual/InverseKinematics.html